Nowadays, in order to monitor a state (such as a speed) of a moving object (such as a vehicle), conventionally a speed sensor (such as a radar) for sensing speed is used. However, since the radar may be inaccurate for sensing a low speed (for example, less than 5 kilometers per hour), the radar has rather limited application. In addition, the radar for sensing speed generally costs expensively in manufacture, installation, testing and calibration, lacking economy and maintainability.
In addition, in the field of fast inspecting a vehicle based on radiation scanning, in order to monitor a state of a subject vehicle, conventionally, a plurality of photoelectric switches or light curtains as well as ground sensor coils are installed in the inspection channel to inspect the travelling state of the subject vehicle. However, since it may be inaccurate to measure a position and a speed of the subject vehicle by utilizing the photoelectric switches or light curtains, mistaken determination are often made about the timing for emitting radiation beams, posing risks to the security of the driver of the vehicle.